Heat oven to 350°F
Coat a 9x13" baking pan lightly with non-stick cooking spray.
Beat cake mix, oil and egg in large mixing bowl, on medium speed until somewhat crumbly. Add peanuts and stir. Measure out and set aside 1 1/2 cups of the cake crumb peanut mixture to be used later. Pour remaining mixture into prepared pan and press out to evenly cover the bottom of the pan.
Beat sweetened condensed milk and peanut butter in a medium bowl until smooth (hint: use the same bowl you used for cake crumbs). Spread this over the prepared cake crust. This will be a bit challenging. Be careful but don't worry if you struggle with the cake layer a bit.
After spreading the mixture sprinkle about 4 oz of semi sweet chocolate chips evenly over the peanut butter mixture.
Pour reserved cake crumb mixture over the top and spread evenly, pressing down gently.
Bake 25 - 30 minutes until set. Remove from oven. Turn oven off. Top with Remaining about 6 oz more of chocolate chips. Return to oven for 1 minute and then remove from oven. Use a spatula to spread the chocolate evenly over the top of the bars. Cool and store in covered container. Enjoy.
Note: You can be creative with this recipe. The cake flavor may be changed. Other flavor chips may be substituted for chocolate. Other nuts may be substituted or combined for/with peanuts. Other nut butters may be substituted for peanut butter. This one basic recipe can produce many bar variations.